The present invention relates to a voice coil motor (VCM) driver and a pulse width modulation (PWM) amplifier, and in particular to a technology effectively applied to a VCM driver and a PWM amplifier used for, for example, a hard disk memory device.
In a hard disk drive device, seek-time needed for movement between tracks tends to be shortened from the viewpoint of high speed access. As a result of this, the drive current of a voice coil motor (VCM) has increased and heat generation at a seek operation has become a problem. In order to solve this heat generation problem, the power consumption is reduced by pulse width modulation (PWM) drive only in the seek period of time when accurate positioning control is not required but power consumption is large. On the other hand, at the time of track following when the magnetic head is allowed to follow a required track for read and write, high-precision control is required for accurate tracking and the influence of a noise caused by PWM drive should be avoided, so that linear drive is used instead of PWM drive. An example of a VCM driver using such a PWM/linear combination method is disclosed in Japanese Patent Laid-Open No. 2002-184137 (Patent Document 1). Furthermore, an example of a VCM driver entirely using PWM drive is disclosed in Japanese Patent Laid-Open No. 2005-304095 (Patent Document 2) and Japanese Patent Laid-Open No. 2005-304096 (Patent Document 3). All of them have been proposed by the present inventors.